1. Field of the Invention
This invention relates to an image processing apparatus and method, more particularly, to an image processing apparatus and method for adding a pattern, preferably one which is specific to a specific apparatus and method, to an image signal.
2. Description of the Related Art
Recent improvements in the picture quality of copying machines and the additional capability to produce color copies have made it possible to obtain copies that are almost indistinguishable from the originals. As a consequence, there is the danger that originals (hereinafter referred to as "specific originals") such as securities and bank notes whose copying is forbidden may be copied unlawfully and that such copies may be put to wrongful use.
If an unlawful copy has been produced, it is difficult with the prior-art techniques to identify, based upon the unlawful copy, the apparatus used to produce it as well as the individual that made the copy.
In order to prevent unlawful copying, attempts have been made to add a pattern (hereinafter referred to as a "specific pattern"), which is specific to the apparatus that produced the copy, to the copy, thereby making it possible to identify, from the unlawful copy itself, the apparatus used in its production as well as the individual that produced the copy.
However, certain problems are encountered in the prior art described above. Specifically, depending upon the image of a specific original or the color of the transfer material used, there are cases in which it is impossible to identify the specific pattern that has been added. In addition, there are cases in which the specific pattern is too conspicuous, thereby detracting from the picture quality of the image output.